Abstract: A gamma ray collimator for use in a cardiac inspections system is disclosed which resolves energetically unperturbed gamma rays emitted from a patient and removes inelastic scattered gamma rays. A plurality of collimator elements each have walls, with each wall defining a plane comprised of a first material layer covered by a second material layer and absorbing inelastic scattered gamma rays, the planes being parallel to a central longitudinal axis in each of the collimator elements. The walls of each collimator element define an elongated longitudinal passageway having open ends through which the energetically unperturbed gamma rays enter and leave. The first material layer has a large absorption coefficient for gamma rays, and the second material layer has a large absorption coefficient for inelastically scattered gamma rays generated in the first material layer responsive to gamma rays emitted from the patient.

Abstract: A transformable gamma camera includes detectors mounted for circumferential movement with respect to a rotating gantry. The rotating gantry includes radial bores at desired angular positions about the rotating gantry. The stationary gantry includes a docking station such as a bore. A coupling mechanism allows the detectors to be coupled to the bores in the rotating gantry or to the docking station. Each of the detectors is movable radially with respect to the rotating gantry's axis of rotation and tangentially to the imaging region. The gamma camera is readily transformable between 120 degree, orthogonal, and opposed detector configurations; a plurality of aperture sizes can also be defined.

Abstract: A gamma camera includes at least one detector assembly 10. The detector assembly includes an array of photomultiplier tubes, a sheet of scintillating crystal material, a sheet of optical glass, and a matrix of mu-metal material. The mu-metal matrix defines an array of apertures corresponding to the array of photomultiplier tubes into which apertures the photomultiplier tubes are inserted. The scintillating crystal is bonded to the first surface of the optical glass. The mu-metal matrix is connected to the second surface of the sheet of optical glass using an adhesive such as an epoxy cement. By integrating the metal matrix into the structure formed by the glass sheet and the crystal, the glass sheet may be made thinner than before while the crystal is supported against possible bending and consequent fracture.

Abstract: A magnet having a yoke and a pair of poles coupled to the yoke in a spaced apart relationship includes a pair of energization coils in proximity to each of the poles for creating a magnetic field of a desired strength. A pair of prepolarization coils are also disposed in proximity to each of the poles to vary the strength of the magnetic field during a nuclear magnetic resonance prepolarization procedure. In order to minimize the amount of eddy currents introduced to the yoke during the prepolarization procedure the poles are comprised of magnetically effective and substantially non-electrically conductive material. Magnetically effective material includes material having a low hystresis. To further reduce the amount of eddy currents introduced to yoke, a flux is created having a sense substantially opposite of that produced by the energization coil. Such opposing flux may be produced by the prepolarization coils and/or by a shield winding placed in proximity of the poles for that purpose.

Abstract: An object (22) is positioned on a patient support (25) between an x-ray source (10) and an x-ray detector assembly (15). The x-ray source (10) is selectively activated to transmit an x-ray beam (20) through an imaging region (32) to the x-ray detector assembly (15). Positioning of the object (22) on the patient support (25) is such that a gap 33 exists in the imaging region (32) through which x-rays may pass unattenuated. An x-ray equalization filter (30) is introduced into the gap 33 and substantially conforms to its shape. The equalization filter (30) comprises a fluid medium disposed in a flexible receptacle. The fluid medium contains x-ray attenuating material suspended in a gel base. Placement of the equalization filter (30) in the gap reduces the number of unattenuated x-rays reaching the x-ray detector assembly (15) thereby enhancing image quality.

Abstract: A method of image reconstruction from wedge beam data includes collecting cone beam data in two-dimensional arrays. The collected data corresponds to rays of penetrating radiation diverging in two dimensions from a common vertex which travels along a curve. Each element of the data is related to line integrals of an object being reconstructed taken along each ray. A local coordinate system is defined having three mutually orthogonal axes and an origin at the vertex. The third axis of the local coordinate system extends in a direction tangential to the curve at the vertex. The collected data is rebinned into a wedge beam format wherein sets of parallel rays are grouped to define planes of radiation that angularly diverge from a common axis. A one-dimensional convolution of the rebinned data is computed in the local coordinate system along a direction parallel to the third axis. Finally, the convolved data is weighted and three-dimensionally backprojected.

Abstract: A localized shim coil (34) for use in a magnetic resonance imaging system includes a plurality of conductive elements (22a-d). The plurality of conductive elements (62a-d) are connected to a current source (64). The plurality of conductive elements (62a-d) are arranged adjacent to a localized region of a subject being imaged such that current flowing through the conductive elements generates a localized magnetic field. A plurality of series connected choke and resister pairs (66a-d) and (68a-d), respectively, are connected to the plurality of conductive elements (62a-d). The chokes (66a-d) present high impedance to currents having frequencies substantially the same as a resonant frequency of the magnetic resonance imaging system. The resisters (68a-d) balance the current flowing through each conductive element (62a-d).

Abstract: A method of designing a shielded gradient coil assemblies (22) for magnetic resonance imaging systems is provided. The method includes generating a first continuous current distribution for a primary coil (60) using an inverse approach. The first continuous current distribution is confined within predetermined finite geometric boundaries of a surface defined by two dimensions and generates a magnetic gradient field across an imaging region (14). The magnetic gradient field constrained to predetermined values at specified spatial locations within the imaging region (14). The current distribution and magnetic field are converted into a stored energy and magnetic field domain where a finite element analysis is performed to generate a second continuous current distribution for a shielding coil (62). The second continuous current distribution is confined within predetermined finite geometric boundaries of a surface surrounding the primary coil (60).

Abstract: A method of image reconstruction from partial cone beam data includes collecting the partial cone beam data in two-dimensional arrays. The collected data corresponds to rays of radiation diverging in two dimensions from a common vertex as the vertex travels along a curve. Each element of the data represents a line integral of an object being reconstructed taken along each ray. The data is then pre-weighted and a local coordinate system is defined. A one-dimensional convolution of the pre-weighted data is computed in the local coordinate system along a direction which is tangential to the curve along which the vertex travels. Finally, the convolved data is weighted and three-dimensionally backprojected. In a preferred embodiment, the curve defines a helical path, and the kernel for the one-dimensional convolution of the pre-weighted data is a ramp convolver.

Abstract: Primary superconducting coils (50) generate a magnetic field through an examination region (10). Stabilizing coils (70) are magnetically coupled with the magnetic field generated by the primary coils. A primary persistence switch (60) and a stabilizing coils persistence switch (72) are opened when the primary coils are connected to a current source (62) to ramp-up the magnetic field. The persistence switches are closed, disconnecting the primary coils from the current source and connecting the primary coils and the stabilizing coils into closed loops. As the magnetic flux generated by the primary coils fluctuates as the primary coils stabilize, the changing flux induces currents in the stabilizing coils. The currents induced in the stabilizing coils generate an offsetting magnetic flux such that the net magnetic flux generated by the primary and stabilizing coils is held constant.

Abstract: An x-ray source (30) transmits a beam of x-rays through an examination region (E). A detector (28), in an initial spatial orientation relative to the source, receives the beam and generates a view of image data indicative of the intensity of the beam received. A first accelerometer (40), capable of generating acceleration data in at least one dimension, is associated with the detector. A second accelerometer (42), capable of generating acceleration data in at least one dimension is associated with the source. A position calculator (60) mathematically calculates a position of both the source and detector based on the acceleration data generated by the accelerometers. An image reconstructor (62) receives the relative position data; electronically corrects for any misalignment or change in beam travel distance, and reconstructs the views into a volumetric image representation.

Abstract: A digital automatic X-ray exposure control system (22, 24, 26) includes a digital frequency modulated output signal circuit (40) generating a digital frequency modulated output signal (42) having a pulse rate that is frequency modulated in proportion to the level of an X-ray beam received at an ion chamber of an X-ray imaging apparatus. A digital input circuit (22) connected to the output circuit via a digital communication interface cable (26) receives the digital output signal and generates an exposure termination signal (80) for use by the X-ray imaging apparatus to interrupt the generation of the X-ray beam at a precise exposure level. The digital input circuit includes a digital counter circuit (70) for counting pulses in the output signal as a pulse count value that is compared against an exposure length parameter value (74) for generating a count match signal (76) based on a correspondence therebetween.

Abstract: A microscope calibrator includes a housing supporting a series of focusing targets each situated at a predetermined distance from one another. Attributes of the microscope are determined by focusing the microscope on one ore more of the focusing targetrs and determining a location of the microscope with respect to the focusing targets focused upon. The position of the focusing targets are determinable by virtue of a local reference frame target attached to the microscope calibrator or by using a tracked probe to communicate the location of each point focused upon by the microscope on each of the focusing targets.

Abstract: An apparatus (1) for supporting a surgical instrument in the operative environment of an imaging device comprises components all made of a material compatible for use in the operative environment of the imaging device. The components of the apparatus (1), made of such a material, include a member (32) that has a spherical surface and includes a bore (50) extending through the member along its diameter. A grip (26) has a grip surface (40) defining an aperture that is adapted to receive the member for rotatable movement within the aperture. The grip (26) extends around the member (32) in a circumferential path and has a gap (42) therein. A fastener (30) is operatively connected to the grip (26). The fastener (30) is adjustable to change the size of the gap (42) and adjust the compressive force applied to the received member (32) in the grip.

Abstract: A continuous CT scanner (10) for producing real time images includes a stationary gantry portion (12) having an examination region (14) and a rotating gantry portion (20) for continuous rotation about the examination region (14). Mounted to the rotating gantry portion (20) is an imaging x-ray source (22) which produces a fan-shaped x-ray beam (24) having a plurality of rays through the examination region (14). A plurality of radiation detectors (28) are mounted to one of the rotating and stationary gantry portions (20, 12) and are arranged to receive rays of the fan-shaped x-ray beam (24) after the rays have passed through the examination region (14). The plurality of radiation detectors (28) converts detected radiation into electronic data wherein the electronic data includes a plurality of data lines in a fan beam format. A rebinning processor (30) interpolates the electronic data from the fan-beam format to a parallel-beam format.

Abstract: A method of designing a shielded gradient coil assemblies (22) with a flared primary coil (60) for magnetic resonance imaging systems is provided. The method includes generating a first continuous current distribution for a primary coil (60) using an inverse approach. The first continuous current distribution is confined within predetermined finite geometric boundaries of a surface defined by three dimensions and generates a magnetic gradient field across an imaging region (14). The magnetic gradient field is constrained to predetermined values at specified spatial locations within the imaging region (14). The current distribution and magnetic field are converted into a stored energy and magnetic field domain where a finite element analysis is performed to generate a second continuous current distribution for a shielding coil (62). The second continuous current distribution is confined within predetermined finite geometric boundaries of a surface surrounding the primary coil (60).

Abstract: A radiation detector includes wavelength-shifting optical fibers which are selected and arranged to capture a greater percentage of visible photons through the use of two or more different color stages of wavelength-shifting fibers. A primary set of optical fibers contains a first wavelength shifting optical fiber tuned to absorb photons emitted by the detector crystal and to re-emit photons at a longer wavelength. At least some of the re-emitted photons from the primary set of optical fibers are captured and transmitted down the first wavelength shifting optical fiber. A secondary set of optical fibers contains a second wavelength shifting optical fiber tuned to absorb photons emitted by the primary set of optical fibers and to re-emit photons at a still lower frequency. In this way at least some of the photons emitted by the primary set of optical fibers and not transmitted down the first optical fiber are captured and transmitted down the secondary optical fiber.

Abstract: An x-ray source assembly (28) includes an x-ray tube with an adjustably sized focal spot (22) for fluoroscopic viewing and radiographic recording. The x-ray source is spaced from an object to be imaged by a first distance (q). An x-ray image receptor assembly is position at a second distance (p-q) away from the object to be imaged. The second distance is greater than or equal to the first distance. A system (40) minifies electronic images from an image receptor (24) for fluoroscopic viewing and radiographic and cineradiographic image recording to a size that is approximately the size of the object being imaged. In this manner, the displayed images have a level of perceived detail that is substantially equal to images generated from radiation receptors positioned contiguous to the subject.

Abstract: After exciting magnetic resonance (60), a train of magnetic resonance echoes including echoes (70.sub.1, 70.sub.2, . . . ) is induced, e.g., with a series of refocusing pulses including pulses (72.sub.1, 72.sub.2, . . . ). The echoes are phase and frequency-encoded appropriately for generating at least first and second images (94, 98). The first image echoes are interleaved with the second image echoes, for example, odd-numbered echoes for the first image and even-numbered echoes for the second image. To select the effective first/second image echo time, the first/second image echo which follows resonance excitation by a time closest to the selected first/second image effective echo time is given the zero or minimum phase-encoding. Nearby echoes being encoded with low phase-encode angles. In this manner, the effective echo times of the first and second images are selected to have preselected relative contrasts of diagnostic interest.

Abstract: A method for shimming main magnetic field in a magnetic resonance imaging apparatus is provided. The method includes generating a radio frequency pulse sequence (200) while a subject is in an examination region (14) of the magnetic resonance imaging apparatus. A reference signal (EC1) which is immune to shim errors is then acquired. Thereafter, a field echo (EC3a) signal is acquired which is sensitive to shim errors. The field echo (EC3a) signal is acquired at a timed interval (T) equal to a multiple of an amount of time it takes for fat and water signals to become in phase. The temporal position of the maximum of the field echo signal is compared to its predicted temporal position (EC3) relative to the reference signal (EC1). The shim term is calculated based on the preceding comparison and an electrical current is applied to one of a gradient offset and a shim coil such that the main magnetic field is adjusted according to the shim term.